Air-break low-voltage circuit breakers need an arc quenching chamber to quench any arcs that occur without impairment of the circuit breaker and adjacent system parts or other components, otherwise, there is a risk that the hot arc gases, which are thus ionized, might cause an electric sparkover or other damage.
Arc quenching chambers can be manufactured only as separate units, in particular for large circuit breakers. The purpose of the arc quenching chambers' connection to the main body of the circuit breaker and connection of individual parts to one another is to seal technically necessary gaps and joints to prevent passage of ionized arc gases and prevent electric sparkover due to any gases that escape nevertheless. In this regard, special attention should also be devoted to the connection of the quenching chamber cover to its housing.
U.S. Pat. No. 4,388,506 describes a quenching chamber which is arranged removably on an air-break circuit breaker.
A quencher is inserted into a groove on a side of a stationary contact by using a hook-like extension and is secured with screws on the side of the movable switch contact. However, quencher cover is attached to a housing of the quencher with four screws. With this switch, the hook-like extension serves to secure the entire quencher and also in particular to seal it against leakage of ionized arc gases.
German Patent No. 35 41 514 describes an arc quenching chamber with an attachment for further cooling of escaping gases. This attachment is mounted on the arc quenching chamber with a total of four screws. These screws pass through holes in a wall of a housing body of the arc quenching chamber, entering pockets that are open at a side. The pockets are designed to accommodate the dimensions of inserted nuts, so that the screws can engage in the nuts with their thread. This arc quenching chamber requires not only four fastening screws but is also complicated and expensive to manufacture, e.g., the pockets that are open at the side to accommodate the nuts.
European Patent Application No. 225 207 describes an arc quenching chamber where arc quenching plates are held between two side walls that are provided with ribs and grooves and have integrally molded half covers for a quencher with an insulating holder. With the help of screws and this holder, the half covers are attached to a bracket, which in turn serves for attachment to a breaker enclosure, which is done with the help of fastening screws. Apart from the multitude of individual parts of the quenching chamber per se, a plurality of fastening elements are needed to attach the quenching chamber to a breaker, namely four screws including washers per breaker pole for fastening the half covers to the two mounting brackets, two mounting brackets, and two screws with nuts for securing the mounting brackets to the breaker enclosure.
With other conventioal breakers, described in German Patent No. 44 10 108, the quenching chamber cover is attached to a quenching chamber enclosure with four screws. The quenching chamber cover covers an extension of the quenching chamber enclosure in which a single fastening screw is accommodated as a captive screw mounting a complete arc quenching chamber on the circuit breaker. An insertion opening for a screwdriver is provided in the arc quenching chamber cover. Here again, a relatively large number of fastening elements are needed for fastening the quenching chamber cover to the quenching chamber and fastening the quenching chamber to the enclosure of the breaker.